Conventional pyrotechnic obscurant compositions have been provided which generate a dense primary particulate, such as inorganic oxides, or compounds which easily form atmospheric aerosols, such as hydrochloric acid, polyphosphates, or phosphoric acid. Further, conventional smoke grenades are well known, which disperse smoke via various types of chemical reaction. Although various smoke-producing compositions and devices are presently known, many such compositions are toxic.
In particular, most conventional smoke-producing compositions incorporate materials which are severely toxic, or are irritants when subjected to the heat necessary to produce smoke. Personnel anticipating exposure to such harmful smoke must protect themselves from the smoke. The problem of toxicity and irritation to people is clearly a limitation in several respects. Not only does it increase the potential for injury, but it may dictate the use of additional specialized equipment, such a respiratory protection. This type of equipment is expensive, and in, for example, training exercises, may detract from the ability to simulate actual conditions.
Additionally, most conventional smoke-producing compositions produce detrimental effects on equipment and supplies. For example, in addition to being toxic and irritating to people, conventional smoke-producing compositions are corrosive and damaging to both mechanical and electronic equipment. This is problematic, as smoke producers are usually employed in field operations which involve the use of precision electronic and mechanical equipment that may be damaged by the corrosive exhaust of such smoke-producing agents. Accordingly, the use of corrosive and damaging chemical compositions is a severe limitation for many known smoke compositions.
For military use, volatile hygroscopic chloride (HC) smokes are important for large scale operations. The most widely used HC type smoke-producing compositions are those resulting in the production of zinc chloride smokes. One example of a military HC smoke composition employs a reaction between hexachloroethane and zinc to produce zinc chloride. However, the reaction products are very toxic and believed to be carcinogenic.
Typical HC smokes have an obscuration index of about 200. Obscuration index is a dimensionless figure of merit for comparing the efficacy of smoke compositions. It compares the transmittance of electromagnetic radiation of a wavelength (or band of wavelengths) at a fixed smoke concentration and pathlength. The following equation, based upon Beer's Law, defines the transmittance of a smoke cloud as a function of mass extinction coefficient, concentration and path length:Tλ(t)=e−αCl.                 where T=transmittance at some wavelength, λ                    α=extinction coefficient, in m2/g,            C=smoke concentration in g/m3, and            L=path length in m.The transmittance is a function of both wavelength and time in a burning pyrotechnic.                        
Other effective smoke-producing compositions are based on phosphorus compounds (particularly red phosphorus) which form phosphoric acid in the atmosphere. Typical red phosphorus (RP) smokes have an obscuration index of about 4000. Although phosphorus smokes are highly effective, the smoke products are extreme irritants and are corrosive. This has led the United States Surgeon General to require the use of gas masks by persons exposed to such smokes. In addition, phosphorus reactions typically produce intense heat which is a further hazard and limitation of this type of material.
There have been recent efforts to develop low toxicity smoke compositions based on organic acids. For example, Douda et al. U.S. Pat. No. 4,032,374 discloses a low toxicity smoke composition based upon cinnamic acid for simulating fires and for training purposes. The cinnamic acid is volatilized by burning a mixture of potassium chlorate and sugar. Other low toxicity obscuring smokes based on aliphatic diacids are disclosed in Shaw et al. U.S. Pat. No. 5,154,782, which is incorporated herein by reference. In general, low toxicity smoke compositions based on organic acids have an obscuration index from about 120 to 140, approximately 60% of the screening power of HC smoke.
Current low toxicity smokes are useful for training purposes, but not for battlefield deployment. This requires the military agency to maintain a training round and a field use round of smoke-producing compositions. It would be a significant advancement in the art to provide low toxicity smoke generating compositions that can be used for both training and field deployment. Reduced inventory costs and ability to train troops in the same smoke environment that would be encountered on the battlefield would be an important advantage.
Further prior art dispersable materials, e.g. tear gas, are dispersed by various techniques. In one technique, the dispersable material is combined with a flammable material. Burning the combined materials vaporizes them, and they thereafter spread as a smoke cloud. In another technique, the dispersable material is packed with an explosive charge which detonates upon impact and causes the dispersable material to spread over an area.
The major shortcomings of these prior art techniques is that the combustion or explosion associated with each technique poses a fire or concussion hazard to buildings, property and people. Further, a container with slow burning contents can be picked up and thrown back at law enforcement personnel. Moreover, although unintentional, an exploding projectile can cause severe injury or even death.
Accordingly, it is an object of the present invention to provide a self-contained grenade capable of controllably dispersing a non-toxic obscurant composition via a thermal reaction.
It is a further object of the present invention to provide a self-contained grenade capable of controllably dispersing an aerosol composition via a thermal reaction.